This research program is designed to study the ultrastructural and functional responses of the rat parotid gland to single and multiple low doses of x-irradiation. Parotid glands of albino rats are being investigated for ultrastructural changes and alterations in protein synthesis following the exposure of the head and neck regions to 500 R..Studies using multiple administrations of x-irradiation are designed to disclose relationships between multiple incidents of subcellular damage, each followed by repair, and the phenomena of cellular aging an neoplastic induction. The tissues of rat parotid glands, irradiated with 500 R and 250 R, were investigated by routine light and electron microscopy. The pathways of synthesis of alpha-amylase,lysosomal enzymes and structural proteins will be studied by high resolution electron microscopy following injection of tritiated amino acids. Parotid glands will be depleted of alpha-amylase by the action of isoproterenol to establish a base line from which amylase reaccumulation can be compared in x- irradiated, sham-treated and untreated control animals.